1. Field of the Invention
This invention relates to an image processing system having image scaling capabilities.
2. Discussion of the Background
Image processing systems may be required to effect image reduction processing and enlargement processing for scaling images to desired sizes. FIGS. 16(A)-16(D) are diagrams that explain the nature of conventional vertical image reduction processing. In the original image shown in FIG. 16(A), image lines numbered 1, 4 and 7 are black and the other lines are white. The reduced image shown in FIG. 16(B) is 0.8 times smaller than the original image.
In the reduced image shown in FIG. 16(B), the lines numbered 1 and 6 of the original image have been dropped and the reduced image is therefore missing one black horizontal line. As can be seen from this example, conventional vertical image reduction processing simply drops a number of lines. Fine line details are therefore sometimes lost. In the reduction of an original image having lines L1-L3 each having a width of one line as shown in FIG. 16(C), for example, the original line L3 may be dropped and completely lost after the image reduction as shown in FIG. 16(D). This problem of line dropping also arises during horizontal reduction.
FIGS. 17(A) and 17(B) are diagrams for explaining the nature of conventional vertical image enlargement processing. The original image shown in FIG. 17(A) is the same as that shown in FIG. 16(A) referred to above. The enlarged image shown in FIG. 17(B) is 1.25 times larger than the original image. The image of FIG. 17(B) includes two additional lines also numbered 0 and 4 of the original image. The width of these lines is therefore doubled. As can be seen from this example, conventional vertical image enlargement processing simply adds a number of lines. The thickness of some of the lines in the image therefore becomes excessively thick. This problem of line addition also arises during horizontal enlargement.
Moreover, the conventional enlargement processing can easily enlarge an image an integer number of times but has difficulty enlarging an image by an arbitrary scale factor including a fractional component.